Academic Social Networking Sites

I'm curious to find out what social networking sites other archaeologists are using. I've built a profile at Academia.edu, which seems to be well designed and quite active. There was an article in the New York Times today lauding the Researchgate.net site. I have an account there too, which I created in response to "friend" requests from colleagues. I find the Researchgate site awkward and cumbersome to use.

There are clearly too many social networking sites out there. I must have profiles on at least half a dozen, and I obviously don't keep up with any of them as a result. What site(s) do you use?